flake8 fixes

a stricter flake8 bump. mostly things around f strings and format
strings, but a couple of bad placeholder names in loops

tests/app/authentication/test_authentication.py

@@ -253,7 +253,7 @@ def test_should_allow_valid_token_when_service_has_multiple_keys(client, sample_
     save_model_api_key(api_key)
     token = __create_token(sample_api_key.service_id)
     response = client.get(
-        '/notifications'.format(str(sample_api_key.service_id)),
+        '/notifications',
         headers={'Authorization': 'Bearer {}'.format(token)})
     assert response.status_code == 200
 

tests/app/broadcast_message/test_rest.py

@@ -412,7 +412,7 @@ def test_update_broadcast_message_status_rejects_approval_from_creator(
     )
 
     assert mock_task.called is False
-    assert f'cannot approve their own broadcast' in response['message']
+    assert 'cannot approve their own broadcast' in response['message']
 
 
 def test_update_broadcast_message_status_rejects_approval_of_broadcast_with_no_areas(
@@ -523,7 +523,7 @@ def test_update_broadcast_message_status_rejects_approval_from_user_not_on_that_
     )
 
     assert mock_task.called is False
-    assert f'cannot approve broadcast' in response['message']
+    assert 'cannot approve broadcast' in response['message']
 
 
 @pytest.mark.parametrize('current_status, new_status', [

tests/app/notifications/test_validators.py

@@ -354,9 +354,11 @@ def test_check_is_message_too_long_passes_for_long_email(sample_service):
     with pytest.raises(BadRequestError) as e:
         check_is_message_too_long(template_with_content)
     assert e.value.status_code == 400
-    expected_message = f'Your message is too long. ' \
-        f'Emails cannot be longer than 1000000 bytes. ' \
-        f'Your message is 1000084 bytes.'
+    expected_message = (
+        'Your message is too long. ' +
+        'Emails cannot be longer than 1000000 bytes. ' +
+        'Your message is 1000084 bytes.'
+    )
     assert e.value.message == expected_message
     assert e.value.fields == []
 

tests/app/service/test_url_for.py

@@ -25,7 +25,7 @@ def test_url_for_get_service_by_id(notify_api):
 def test_url_for_create_service(notify_api):
     with notify_api.test_request_context():
         url = url_for('service.create_service')
-        assert str(url) == '/service'.format(service_id)
+        assert str(url) == '/service'
 
 
 def test_url_for_update_service(notify_api):